I also ran into the problem trying to place a maneuver node but couldnt. I'm done with the cheating now I have the hang of things better. So I ended up burning up way too much fuel just to get there. I didnt plan anything out, and I really didn't want to time accel to get the optimal planetary config to give the least amount of DeltaV to get there. I ended up short on fuel because I just randomly chose a target right after achieving Kerbin orbit. On both tours I had enough to do things I wanted to, but didn't have enough fuel to get back to Kerbin.so I ended up editing the save file to give me a full tank on the way back.

My main goal with the flights were to get experience in transfers and finding my way back. I had enough fuel to get there, but didn't really care about having fuel to get back because. I did a tour of some of the inner planets, and then on my next mission went to Duna, and ended up intercepting Ike first and landing, and did a flyby of Duna on the way out. Of course if I watched all of his videos I could also, but he sometimes goes way too fast with things). I basically cribbed a rocket from one of Scott Manley's videos (note: I haven't watched many of his videos, and it is frustrating watching some of his videos because he just does things assuming you know almost as much as he does. Couple of nights ago I started playing around with some interplanetary missions.

Kerbal space program free return duna